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Geriatric HIMS in Small-Breed Dogs: A Retrospective Look at a Common but Overlooked Syndrome
Dr. Keith A Hnilica, DVM, MS, DACVD
Apr 14, 2026
6 min read
A retrospective review of 450 small-breed dogs between 8 and 17 years of age suggests that geriatric HIMS—hormone imbalance with melatonin sensitivity—may represent a common, previously undescribed clinical syndrome in older dogs that has often been lumped under the vague label of “atypical Cushing’s.” These dogs, all under 30 pounds and of mixed sex, shared a striking pattern of clinical decline: geriatric slowing, potbellied appearance, polyuria and polydipsia, cutaneous atrophy, recurrent secondary skin infections, and worsening allergic disease. Taken together, the pattern points not just to aging, but to a broader state of hormone imbalance, inflammation, and immune dysregulation.
What makes this group especially interesting is how consistently many of these dogs responded to therapy. All dogs in the review were placed on high-dose melatonin each evening for 30 to 45 days. Approximately 80% showed significant clinical improvement. Owners and clinicians reported better overall function, fewer and less severe infections, reduced allergy symptoms, and improved quality-of-life scores. That degree of response suggests this is not simply “normal aging” and may instead reflect a biologically meaningful syndrome with a recognizable treatment response.
The findings also highlight how much remains unknown. Only about 10% of the dogs underwent a complete diagnostic workup for Cushing’s syndrome, which limits conclusions about how this condition overlaps with or differs from classic and atypical hyperadrenocorticism. Future prospective studies with standardized endocrine testing, inflammatory markers, and long-term follow-up are needed.
Even so, this preliminary retrospective dataset raises an important possibility: many older, small-breed dogs currently described as having vague geriatric decline or atypical Cushing’s may actually be experiencing geriatric HIMS. If confirmed, this would give veterinarians a more practical framework for recognizing a common syndrome that appears clinically important, treatment-responsive, and highly relevant to everyday small-animal practice.